TORPEDOES OF THE IMPERIAL JAPANESE NAVY

Part One: Through 1918

Soon after the United States and Japan became involved in World War Two, the Allies learned through disastrous experience that the Imperial Japanese Navy was well prepared in many ways for a major naval war. One of the surprises was that torpedo warfare was a major strength and that strength encompassed doctrine, tactics, and weapons. It was eventually learned that Imperial Japanese Navy torpedoes far outperformed anything the Allies had. The details of these weapons will be discussed in a subsequent article. As a preliminary, however, it is useful to explore how torpedoes evolved in the early years of the Imperial Japanese Navy.

Robert Whitehead’s first successful automobile torpedo was built in 1868, the same year that the Imperial Japanese Navy was born. The original torpedo consisted of a fusiform shell 14 inches in diameter and about 11 inches long which comprised the main structural member. Within the shell there was a) a warhead with a forty-pound high explosive charge, b) a flask or tank containing compressed air that provided the propulsive energy, c) a small reciprocating engine is driven by compressed air with a small propeller attached to its shaft to provide propulsive power, and d) a surprisingly sophisticated depth control system, which used hydrostatic depth error to control one set of movable elevator fins and pitch angle, measured by a pendulum, to control another set with the combination making a stabilized closed-loop system. External features included vertical fins, running almost the full length of the torpedo, whose purpose was to stabilize motion in the horizontal plane and compensated for the torque of the propeller, the elevator’s fins, and, of course, the propeller. The automobile torpedo was widely regarded as a great equalizer. Small navies saw it as a low-cost means to naval power; large navies viewed it. with great trepidation. as a threat. At both ends of the naval power spectrum, the torpedo was an essential weapon.

Torpedo technology developed rapidly and by the early 1880s, the 14-inch torpedo had grown to about 14 feet in length. The single propeller had given way to a counter-rotating pair. The long vertical fins had disappeared. Engines and compressed air supply had been improved to yield faster. longer-ranged weapons. Two firms, Whitehead in Fiume. Austria and Schwartzkopff in Berlin. with few restrictions sold torpedoes on the world market. About a dozen navies had purchased Whitehead torpedoes and manufacturing licenses. A few navies had purchased Schwartzkopff torpedoes and a few other had developed independent torpedo manufacturing operations usually based on Whitehead licenses. Torpedoes were thus well established in most navies. One exception. however. was the Imperial Japanese navy (another was the United States Navy). Little or nothing was done about torpedo warfare by the Imperial Japanese Navy until the early 1880s. At that time the Japanese Navy was still well behind other navies in this and other technologies and needed a strategy for catching up. This strategy had to take into account the need to develop an industrial base as well as understanding the technology. An examination of the history of the acquisition of torpedoes by the Imperial Japanese Navy shows that the strategy. whether formally stated or not. had four requirements that were satisfied by appropriate actions:

This strategy was followed beginning with the purchase of standard Schwartzkopff torpedoes in 1884, the purchase and licensed manufacture of Whitehead torpedoes, modification of Whitehead designs, and a series of original designs culminating in huge oxygen torpedoes with very large warheads, high speed, and very long range.

This approach to achieving technological competence was practiced in other areas as well, and it was in many ways a national technology strategy. Given the circumstances, one must appreciate that as long as weapons could be purchased and technology licensed, the approach was very sound, efficient, and effective. The technology acquisition strategy was accompanied, especially during the 1930s, by very strict naval security with the net result being unpleasant surprises, alluded to above, for the Allied Powers in WWII.

Japanese Torpedoes

In the course of its history, the Imperial Japanese Navy acquired at least 30 distinct Types of torpedoes for service use. The type number was derived from some significant year in the torpedoes history, purchase, test firing, approval or service us, etc. Some of these Types had variants designated in various ways, and added letters and/or numbers or appended model and modification numbers, much as RN torpedo Marks carry asterisks and USN Marks carry Mods. In five cases there were torpedoes of different diameters with the same type number. The full designation should be 45 cm Torpedo Type 43 or 21-inch Torpedo Type 43, to give an example of the dual use of a Type number. The first Japanese Navy torpedo armament consisted of 14-inch torpedoes acquired from foreign sources. As soon as large 45 cm2, torpedoes became available they became the preferred weapon. The 45 cm torpedoes were in tum displaced, first in surface vessels and later in submarines, by 21-inch torpedoes. After the First World War 24 inch torpedoes were developed for surface ships while 21-inch torpedoes remained standard for submarines. Eighteen-inch torpedoes reappeared as air-launched weapons beginning in 1931 and in the late ’30s and early ’40s as weapons for MTBs and midget submarines. A gross examination of torpedo acquisition reveals another aspect of Japanese naval materiel strategy, the focus on extremes, largest, fastest, longest range, largest warhead, etc.

Japanese torpedoes which were acquired before the end of the First World War are listed in Table 2. The first group consists of seven varieties of 14-inch torpedoes. The Imperial Japanese navy negotiated with both Schwartzkopff, Berliner Maschinenbau AG (BMAG), and Whitehead for the acquisition of their first torpedoes. Schwartzkopff was selected because of its use of corrosion-resistant bronze compressed air cylinders and because of more favorable contract terms. Two types, designated Types 84 and 88, were purchased from BMAG. Later three types were purchased from Whitehead Fiume, the Austrian firm, and two from Whitehead Weymouth, the English firm.

All seven types of 14-inch torpedoes were cold runners, that is, they used only the energy stored in compressed air to drive engines that provided the propulsive power. The engines were all three-cylinder radial types based on the design developed by Peter Brotherhood and modified by Whitehead and Schwartzkopff. The propulsive performance of the Whitehead torpedoes was clearly better than that of the older Schwartzkopff design, but he was simply the general evolution of torpedo design, in particular the increased weight of compressed air. The performance of 14 inch Whitehead torpedoes did not improve much in the few remaining years during which they were procured. One interesting feature of the Japanese torpedoes is the inclusion of a low 11 or 12 knot, speed 2500 meter setting. The long-range was made potentially useful by Whitehead’s incorporation of the Obry device which uses a gyroscope to keep the torpedo on a steady course. Twenty-five hundred yards was an extraordinarily Jong range for the time and probably represents one of the precursors to the .. outranging the enemy” concept that later, between the world wars, played such an important role in Japanese naval thinking.

The 14 inch torpedoes were all about 15 feet long and except for the first Schwartzkopffs carried a charge of 50 kilograms of wet guncotton. The Imperial Japanese Navy probably acquired somewhat over a thousand 14 inch torpedoes. These torpedoes were not substantially different from those of the same size acquired by other navies, but other navies were already acquiring larger torpedoes. The Royal Navy, the German navy and the U.S. Navy were all acquiring 45 cm torpedoes and such torpedoes could be purchased from Whitehead. At this point in time, Japanese torpedo technology lagged-they had learned to build torpedoes in their own shops, but had not yet mastered the design process. For a navy that started from scratch in 1868, that was, nevertheless, fantastic progress.

The next group of torpedoes in the table is best identified as early 45 cm (18 inches) torpedoes. This distinguishes them from a group of air-launched and high-performance 45 cm torpedoes which were developed between 1931 and 1944. The 10 early 45 cm torpedoes introduced between 1897 and 1911 were part of the evolutionary development of Japanese torpedo armament-larger torpedoes with larger warheads, higher speeds, and longer ranges. The early 45 cm group is particularly interesting because within it one sees the first indigenous design for an Imperial Japanese Navy torpedo (Type 38-1), four-cylinder radial engines (Type 38-2A), the transition from cold running torpedoes to dry heaters (Type 38-28) and the final transition to wet heater, or steam, propulsion plants (Type 44-2). All ·of the 45 cm torpedoes as well as the last four 14 inch Types incorporated the Obry device for gyroscopic course control.

There were, however, some other interesting developments. The 1901 45 cm Type 34 (Whitehead) was 6.5 m long, as compared to a nominal 5.0 m for the others, and obtained two to two and a half times. the range of the shorter torpedoes. Such a design would be again at least partially consistent with the larger war-head, faster, longer-range objectives of the Imperial Japanese Navy. The speed was not increased probably because that would have required a new engine design or improved propulsive efficiency, but it is not clear why a larger warhead was not incorporated especially since one had already been developed for the 18 inch Type 30. The 6.5-meter length was not adopted for subsequent 45 cm torpedoes probably because it was not strong enough in the longitudinal bending mode to survive the inevitable rough handling to which torpedoes are subjected.

The 1904 Type 37 was not a strict copy of a Whitehead design. It was, however, sufficiently closely based on the Whitehead 45 cm Type 32 and Type 34 designs that it should probably be classified as a modification rather than in independent design. This torpedo was produced mainly in Japanese Navy shops. The 1905 Type 38-1 was, however, designed and produced at Kure Naval Arsenal. It was not a copy of a Whitehead design and so we concur with Kaigun Suiraishi and classify it as an indigenous design (the first). We note, however, that this torpedo carried a substantial design heritage from long experience with Whitehead torpedoes.

The 1905 Whitehead Type 38-2A torpedo introduced a new four-cylinder radial Brotherhood type engine. This engine was developed as part of the transition to heated air propulsion, but the Type 38-2A was a cold runner, the last of that type adopted by the Imperial Japanese Navy. The 1905 Type 38-28 torpedo was designed and produced by Whitehead and also produced at several Japanese Naval Arsenals. It, and the very similar 1909 Type 42 (also Whitehead”), both employe.d dry heater power plants. These plants heat the compressed air before it enters the engine and thus add thermal energy to that stored in the compressed air. The source of the thermal energy is the combustion of hydrocarbon fuel (or alcohol). A typical hydrocarbon fuel together with the air required for combustion stores in excess of ten times more energy per kilograms than compressed air. Further, the higher engine inlet temperature enhances the thermodynamic efficiency of the engine. Collectively, the result is a torpedo with a longer range or a large warhead at the same total weight. If the engine can operate at higher pressure and temperature, the horsepower and consequently the maximum speed can also be increased. The Type 38-2B torpedo was rated at 3000 meters at 28 lets as compared to 3000 meters at 20.3 kms for the cold running Type 38-2A, which was, except for the heater, identical. There were three Japanese 45 cm dry heater torpedoes, Types 38-28, 42, and 43, which were generally similar. They were a little over 5 meters (16 ft 5 inches) long, weighted about 650 lb, carried 95 kg warheads, and used the four-cylinder Brotherhood engines.

The introduction of dry heaters was a major development in torpedo technology, however, the process did not optimize the available energy for a given total weight of air and fuel, and even at sub-optimal conditions, the high temperatures eroded both durability and reliability of the power plant. Some consideration was given to reducing the engine inlet temperature by externally cooling the combustion chamber, but energy removed in cooling would be wasted. The solution was to inject water directly into the combustion chamber in the wet heater torpedo. The injected water flashed into steam, which together with the heated compressed air and combustion products provided the energy to drive the engine. Such torpedoes came to be known as steam torpedoes and that has persisted. The first Japanese steam torpedo was a Kure design designated 45 cm Type 44-2. Mitsubishi produced 526 of 4000 m at 36 k, a very substantial improvement over the Type 42. Simultaneously with the acquisition of the last 38-inch dry heater torpedo and the first 45 cm steam torpedo, corresponding 21-inch torpedoes were acquired. Attention quickly shifted to these larger torpedoes and further 45 cm torpedoes were developed until 1937.

The first 21-inch Japanese torpedo appears to have been the 21 inch Type 43 manufactured by Whitehead and adopted by the Imperial Japanese Navy in 1910. Other than dimensions and the fact that it had a dry heater propulsion system, only sketchy information has been found about either this torpedo or, as noted earlier, its smaller sibling, the 45 cm Type 43. All of the other Imperial Japanese Navy 21 inch service torpedoes (six types) were designed and produced by the Naval Arsenals and Japanese commercial firms such as Mitsubishi. The first of these were the 21 inch Type 44-1 (1911) and the 21 inch Sixth Year Type (1917). In terms of specifications, these two torpedoes were very similar, with the Sixth Year Type being about 6 inches longer than the Type 44-1, carrying a heavier explosive charge and using higher pressure air. Both torpedoes were conventional wet heater steam torpedoes using four-cylinder radial engines. They achieved a maximum speed of 36 k and a range of 7000 m (7650 m Sixth Year Type) at that speed. This performance, as shown in Table 2, was comparable with that of the best 21-inch torpedoes developed at about the same time by other navies.

The 21 inch Sixth Year Type was the last torpedo developed by the Imperial Japanese Navy before the end of the First World War. In the years between the wars and during WWII additional 21-inch torpedoes, huge 24-inch torpedoes, and modem 18-inch torpedoes for aircraft, patrol boats, and midget submarines were developed. A great technological step was taken in the development of operational torpedoes using pure oxygen rather than air in the combustion process. These, in some cases phenomenal, weapons and the technologies will be discussed in a subsequent article.

Combat Use of Torpedoes by the Imperial Japanese Navy Through 1918

The combat use of torpedoes requires not just the torpedoes, but also launching capability and trained personnel. The Imperial Japanese Navy worked as diligently at these requirements as they did at the torpedoes acquisition. The first Imperial Japanese Navy warship capable of launching torpedoes appears to have been FUSO which was completed in 1878. As completed she was equipped with towed torpedoes, but no launching gear for self-propelled torpedoes. HIEI and KONGO also completed in 1878. All three were fitted with Schwartzkopff tubes for 14-inch torpedoes in 1885-86.6 The first four Imperial Japanese Navy torpedo boats were completed in 1880. These four boats were originally equipped with spar torpedoes, but there were refitted first with “torpedo launching cases/boxes”, about which no further information has been found, and later with torpedo tubes. The first 50 Schwartzkopff torpedoes were delivered in March of 1884. In January 1886 FUSO conducted experimental torpedo firings against a stationary target.7 These tests were reported as successful, but it seems probable that the torpedoes were damaged on impact with the water. Spoons, essentially extensions of the upper half of the tube, were added to the torpedo tubes and fully successful launches were made in October 1886.8 The same source indicates that FUSO fired torpedoes at moving targets in 1888, and that torpedo boats fired at moving targets in 1893. The first five imperial Japanese Navy submarines, Holland boats, were completed in 1905. Each had one 45 cm torpedo tube and practice torpedoes were probably fired soon after the boats were commissioned.

Japanese naval forces were involved in two wars prior to WWI, the Sino-Japanese War (1894-95) and Russo-Japanese War (1904-05). Automobile torpedoes, as opposed to towed or spar types, were used by both sides in both of these conflicts. The results were mixed. In the Battle of the Yalu, 17 September 1894, Chinese vessels fired Schwartzkopff torpedoes at ships of the Japanese fleet without effect. The torpedoes were fired at long range and apparently had poor or poorly maintained depth gear. At least one torpedo was reportedly fired at short range (about 40 yards) and went under its target. In early February 1895 Japanese torpedo boats made night attacks on the remnants of the Chinese fleet in the harbor at Weihaiwei. At least two hits were scored on the battleship TING-YUAN and a cruiser was damaged by torpedo hits. These results were not spectacular, but the torpedo actions represent the use of torpedoes on a larger scale than had been seen earlier.

The Russo-Japanese War, 1904-05, saw further growth in the use, if not the effectiveness, of torpedoes. The first torpedo action of the war, which took place 8-9 February 1904, again before formal declaration of war, was a Japanese attack on the Russian Pacific Fleet at Port Arthur. During this attack, ten destroyers fired a total of about 20 torpedoes. Four hits were scored seriously damaging two Russian Battleships and a cruiser. Torpedo’s attacks against ships at Port Arthur continued until it surrendered in January 1905. Jn these attacks, the largest use of torpedoes against a single target was the remarkable expenditure of 85 in repeated attacks on the battleship SEVAST APOL. Four hits were scored, but the ship was eventually sunk by scuttling. The Battle of the Yellow Sea also saw some notably ineffective use of torpedoes. Japanese vessels fired a total of 74 and scored no hits. The great fleet action of the Russo-Japanese War was the Battle of Tsushima. In this battle, the Imperial Japanese Navy gained nearly absolute control of the seas surrounding Japan. Our interest is not, however, in the entire battle, but in the use of torpedoes. It appears that the torpedoes fired by the Imperial Japanese Navy at Tsushima totaled somewhere between 60 and 1009 including 50 to 90 fired by destroyers and torpedo boats and a few fired by larger vessels. The results were not insignificant. Torpedo attacks were responsible for or played a significant role in sinking three battleships and two armored cruisers of the Tsarist navy. In the entire war, the Japanese navy fired about 250 torpedoes which sank or seriously damaged perhaps ten Russian ships. This far exceeded any previous use of torpedoes both in number and in the damage inflicted by them. For a weapon from which the Imperial Japanese Navy had expected much, however, it was disappointing. Postwar analysis revealed that the confusion of battle, especially night battle, was large and required training that was not provided by stereotyped exercise. The Japanese navy adopted a train as you fight approach, which, while brutal, stood them in good stead in later years. It is worth noting that up to the beginning of the First World War, the Japanese navy had fired more torpedoes against enemy targets than all of the other navies of the world combined.

Japan declared war on Germany on 23 August 1914. The Imperial Japanese Navy chased German surface raiders, invaded German colonies in the Pacific, and contributed to convoying in the Indian Ocean. Jn addition, they provided a cruiser, 12 destroyers, and manning for two others in the Eastern Mediterranean where they were part of the escort and ASW forces. There is no indication that any torpedoes were fired by Japanese forces during the war.

Summary

The Imperial Japanese Navy came into existence in 1868 and quickly began developing a cadre of skilled officers and acquiring modem weapons. In many cases weapons were acquired following a sequence consisting of 1) importing foreign weapons, 2) developing the capability to manufacture these weapons and manufacturing them under license, 3) modifying the foreign designs to gain design experience, 4) developing and manufacturing indigenous designs. Torpedoes were a particularly clear example of the application of this strategy. Fourteen-inch torpedoes were used as purchased and/or copied at Kure. Most 45 cm torpedoes were also foreign designs, but several Types were manufactured in Japan, one significant modification of a Whitehead design was made and two indigenous designs were developed. The cycle was further shortened for 21-inch torpedoes where only one foreign torpedo (the Whitehead 21 inch Type 43) was acquired for service use. The indigenously designed and manufactured 21 inch Sixth Year Type was comparable to the best of its contemporaries (of Table 2). By the end of WWI, Japanese torpedo technology and manufacturing had clearly reached parity with that of the major navies of the world and was developing rapidly, though these facts may not have been recognized by the major navies. The Sino-Japanese and Russo-Japanese wars had provided combat experience in the use of torpedoes. While the effectiveness was less than had been expected, valuable lessons about the problems of torpedo attacks were learned. The Imperial Japanese Navy had fought and won the greatest battle between fleets of armored vessels that had taken place before WWI. Torpedoes had been used successfully against some major warships. While other navies had more torpedo boats, more submarines, and more large vessels with torpedo tubes, the Imperial Japanese Navy had excellent weapons and the edge inexperience. Although the Imperial Japanese Navy apparently did not fire any torpedoes during WWI, Pearl Harbor and early battles at sea proved that by 1941 they had made enormous progress. That progress will be the subject of a subsequent article.